Solid polymer electrolyte fuel cells employ a membrane comprising a solid polymer electrolyte disposed between two porous electron and proton conductive electrodes, the anode and the cathode compartments. The anode and cathode compartments include catalyst layers, gas diffusion layers, and electron conductive flow field plates. Fuel is fed into the anode flow field, diffusing onto the porous catalyst layer, and is oxidized to produce electrons, protons, and CO2 as a by-product when methanol aqueous solution is used as fuel. The polymer electrolyte membrane is proton conductive allowing the protons to migrate towards the cathode. At the same time, oxidant is fed into the cathode compartment wherein the oxidant diffuses onto the porous cathode catalyst layer and reacts with the protons and electrons, producing water as a by-product. The electrons travel from the anode to the cathode through an external circuit, thus producing the desired electrical power.
In stationary applications, fuel cell systems may be required to operate continuously for a period of time. However, in portable or traction power applications, fuel cell systems may be subjected to frequent start-up and shut down cycles. In either case, the fuel cell is expected to provide a reliable power output under specified conditions. Unfortunately, the power output of the fuel cell decreases with operation time under the same operating conditions. For example, fuel cell or stack voltage decays with time at a given operating current density, or vice versa. This cell or stack voltage decay obviously affects overall fuel cell efficiency. More importantly, it may limit fuel cell applications. Therefore, the recovery of fuel cell performance after a period of operation or bringing a fuel cell to a starting up condition after a period of operation is very important in a fuel cell application.
A need exists for a method for regeneration of performance of a fuel cell, typically a liquid feed fuel cell, after a period of operation and a method for start up of a fuel cell system after a period of operation.